The distribution of sound, such as background music and paging announcements, throughout spaces such as office complexes, churches, schools, entertainment parks, government buildings, transit parks, and the like has long been one of the tasks of sound system designers and the architects who design such facilities. One traditional method of distributing sound throughout such facilities has been simply to mount an array of cone-type loudspeakers in the suspended ceilings of the facilities and connect the speakers to an audio amplifier driven by a music and/or paging, masking sound, or other sound source. In many cases, paging and masking sound has been distributed throughout a facility with separate sound systems, although in some cases these functions have been integrated into a single system.
While traditional methods of sound distribution throughout a space has been somewhat successful, they nevertheless are plagued with inherent problems. These problems include, among others, the generally low fidelity of the resulting sound, the difficulty of reconfiguring the speaker array when a floor plan changes; the inherent directional and non-diffuse character of the sound produced by traditional cone-type loudspeakers, which can be distracting; relative loud and quiet areas as one moves about the space; interference patterns as a result of the spaced-apart speakers producing correlated sound; and the changing and sometimes harsh sounding characteristics of the audio program with varying room acoustics within the space. Some of the problems associated with cone-type loudspeakers have been addressed by the assignee of the present invention and others through the development of flat panel sound radiators, which fit within the grid of a suspended ceiling and visually are virtually indistinguishable from a traditional ceiling panel. Pending U.S. patent applications owned by the assignee of the present invention entitled Flat Panel Sound Radiator with Enhanced Audio Performance, Flat Panel Sound Radiator with Bridge Supported Exciter and Compliant Surround, and others disclose such flat panel sound radiators, and their disclosures are hereby incorporated by reference.
Distracting noise in the workplace is not a new problem, but is one that is garnering increasing attention as workplace configurations and business models evolve. A number of recent studies indicate that noise, and particularly conversations of others, is the single largest distraction within the workplace and has a significant negative impact on worker productivity. As the service sector of the economy grows, more and more workers find themselves in offices rather than manufacturing facilities. The need for flexible, reconfigurable space for these workers has resulted in greater use of open plan workspaces; large rooms with reduced ceiling height and moveable re-configurable partitions that define the workstations or cubicles for workers. Unfortunately, distracting sounds tend to propagate over and through the partition walls to disturb workers in adjacent workstations. In addition, the density of workstations is increasing with more workers occupying a given physical space. Further, more workers use speakerphones and conferencing technologies, and computers with large sound reflective screens, personal sound systems, and even voice recognition systems for communicating vocally with the computer. All of these factors, and others, have contributed to the progressive increase in the level of distracting noises and their corresponding negative impact on productivity within the workplace.
Generally, two approaches have been taken to mitigate the presence of distracting sounds in a space. The distracting sound either can be attenuated as it travels from its source to minimize its intrusion into adjacent spaces or it can be covered up or masked by introducing acoustically and spatially tailored masking sounds into the space. Sound attenuation is not always practical or effective, especially in workspaces made up of partitioned cubicles and open doorways and hallways. As a result, electronic sound masking techniques increasingly have been employed to mask and neutralize distracting sounds. A recent paper asserts that:                Sound masking systems are one of the more critical elements in preventing conversational speech from being a distraction in the work environment. They are necessary even when high performance ceiling systems and furniture systems have been installed because they ensure that when the variable air volume systems are moving low quantities of air, enough background ambient sound is present to prevent conversations from being overheard and understood. Sound masking provides electronically generated background sound to achieve normal levels of privacy. (Excerpted from Sound Solutions, a professional paper sponsored by ASID, Armstrong World Industries, Dynasound, Inc., Milliken & Co., and Steelcase, Inc.)        
The principles of sound masking involve the introduction into a space of sound that is tailored to mask the targeted distracting noises. The introduction of masking sounds with a predetermined frequency profile within the frequency spectrum of the human voice, for example, provides a masking effect, in essence drowning out distracting human conversations. A typical sound masking system may include a “pink noise” or “white noise” generator, an audio amplifier and frequency filter set, and a system of connected loudspeakers arrayed throughout the space to reproduce the masking sounds and generally to create a uniform sound field within the space. In fact, uniformity of the masking sound field is a key factor in rendering the masking sounds unobtrusive to occupants. To this end, many traditional masking sound systems include cone-type loudspeakers positioned in the plenum space above the suspended ceiling. In this way, it is hoped that the sound will be diffused as it is reflected off plenum structures and transmitted through the ceiling tiles into the space. Unfortunately, the quality and sonic characteristics of the resulting sound field are generally poor, unpredictable, change with the configuration and contents of the plenum space, change with the type of ceiling tile, and cannot easily be tailored to compensate for the spatially varying acoustic response of the space below the suspended ceiling.
The use of flat panel sound radiators, mentioned above, in sound masking systems can enhance the ability to produce a diffuse and uniform masking sound field within a space and thus can solve many of the problems of traditional plenum mounted masking sound systems. This is due in part to the distributed mode reproduction of such radiators, which results in a less directional sound field, as opposed to the pistonic mode reproduction of traditional cone-type loudspeakers, which results in a more directional sound field. Further, since flat panel radiators project sound directly into a space rather than into the plenum above a suspended ceiling, the prospect of tailoring the sound produced by the radiators to compensate for varying acoustic properties of the space is viable. Flat panel radiators projecting diffuse sound directly into a space provides numerous other opportunities for improvements over traditional masking sound and audio distribution systems, as will become more apparent as the present invention is disclosed below.
While much research and development has been directed to the implementation of masking sound in the workplace to mask distracting noise, prior art implementations still have had significant shortcomings. For example many systems have used so-called “white noise” as the masking sound. Generally, white noise is sound characterized by an equal power distribution as a function of frequency within a particular audio spectrum of interest, and has a characteristic “shhhhhhhh” sound. The problem with white noise is that the human ear perceives the equal power spectrum as being louder at higher frequencies than at lower frequencies, and thus the white noise can itself be distracting or annoying to workers within a workspace. Further, white noise does not follow well the loudness distribution in the frequency domain of typical human speech to be masked, and thus the masking effect varies with frequency.
Most have attempted to address these problems by filtering the white noise in an attempt to replicate in the space a masking sound having a so-called equal loudness or NC40 distribution to produce masking sound characterized not by an equal power distribution but rather by an equal perceived loudness distribution as a function of frequency. While NC40 filtered masking sound is somewhat more efficient at masking distracting sounds, and particularly human speech, the inventors have discovered that it can have an annoying effect upon persons within the space, particularly after prolonged exposure. It is believed that this results from a power or level distribution that is increased at the low and high frequencies and that is decreased at mid-level frequencies. In addition, NC40 filtered masking sound generally requires a slightly higher decibel (dB) level for effective masking of the human voice. For these and other reasons, equal loudness or NC40 filtered masking sound has not proven optimum for masking sound applications in workspaces.
There exists a need in the field of sound distribution for an integrated masking sound, music, and paging system and methodology for buildings such as office spaces that addresses and solves the problems and shortcomings of traditional, often discrete, prior art systems. More specifically, such a system should take full advantage of modern high fidelity flat panel sound radiator technology to produce a diffuse and consistent sound field within a space, especially when reproducing masking sounds, and to produce high quality background music and paging. Masking sounds should be carefully tailored to provide optimum masking of human speech and other distracting sounds within the space with a minimum dB level and without the masking sounds themselves being distracting or annoying to workers, as can be the case with pink and white noise and NC40 filtered masking sound. The audio quality of music and paging sounds should be high fidelity, regardless of the acoustic characteristics of the space itself, and should be consistent sounding as one moves through areas of the space having differing or varying acoustics. For instance, if one moves from an acoustically reflective zone of the space to an acoustically absorptive zone, music and paging sounds should not change from a bright sound to a dull sound and the perceived level of the sounds should remain the same. The system for implementing the needed functions should be pre-engineered, highly integrated into easily installed, easily set-up, easily controlled, and easily adjustable components. Control and adjustment of sound affecting parameters should be provided either by local access, preferably through a computer based graphical user interface (GUI), or from a common telephone, which may be located either on site or at a remote location. The system should include extensive self diagnostic capabilities for monitoring the internal condition of electronic components and software and for diagnosing external wiring and installation related problems throughout the system. It is to the provision of an integrated sound distribution and masking sound system and methodology that addresses these and other needs that the present invention is primarily directed.